A vehicle driveline transmits torque from an engine or motor to one or more wheels. Automotive drivelines sometimes include rear or front drive units, and power transfer units (PTUs, also known as power take-off units) for selectively distributing torque among shafts in the driveline. Two shafts of the PTU or other driveline device may need to be coupled together and the relative axial movement of the shafts constrained by a coupler. Packaging in automotive drivelines, as elsewhere in automobiles, often demands inflexible size constraints which can frustrate or prevent installation of the shafts and any coupler on the shafts, or require a coupler of a size and shape that may be damaged (e.g. plastically deformed or broken) during installation. Further, some connections are done blind, that is, the area of the connection between the shafts is not accessible or visible during assembly. This may be due to, for example, components that surround or enclose all or part of an area outboard of the connection between the shafts.